[install] Notes on OCaml versions and Coq configuration


It seems as of a few months ago 4.07*-flambda images have been removed from Docker Hub for coq:dev

In light of this change, can this post and this wikipage be updated on what is the preferred OCaml version? I see both 4.12 and 4.13 available for coq versions 8.13+, but 8.12 has only up to OCaml 4.11.

cc: @erikmd

The wiki page has been updated now.